The Causes of Down Syndrome
In the process of reproduction the egg cell and the sperm cell begin with 46 chromosomes. As the cells divide they are left with 23 chromosomes each. Thus in the process of fertilization 23 chromosomes of the father’s sperm and 23 chromosomes of the mother’s egg are involved that finally develops to form a fetus and there on begins the process of creation of a baby.
This natural process is sometimes eroded and the sperm or the egg instead of retaining one copy of chromosome number 21 keeps both copies. This causes an additional copy of chromosome to be retained inside taking the total count of chromosome number 21 to 3 instead of two. This ends up in building an extra copy of chromosomes in all the cells in the body of the child, leading to a major defect called the Down syndrome.
This abnormality in fertilization can occur in three patterns. It can cause from ‘trisomy 21′, which is most common. This is formed due to retaining of that one extra copy of number 21 chromosomes. Thus the child will have three copies of chromosome 21 in every cell in the body. Further, an abnormal division of cells subsequent to fertilization can happen whereby the child has extra copy of number 21 chromosomes on some cells and not all. This is called Mosaic Down syndrome. Another fertilization process away from the natural could be when Translocation Down syndrome where at conception stage or even before 21 number chromosome gets ‘translocated’ or attached to another chromosome.
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